The present invention relates to a hard disk drive or other data storage device, and more particularly to the supply of voltage to a write circuit for writing data onto a magnetic disk.
A hard disk drive is one of the most widely used external storage devices for a computer. As is generally known, a magnetic disk, which is used as a storage medium for the hard disk drive, uses sectors as minimum data recording units. The sectors are obtained by radially dividing tracks that are obtained by concentrically dividing the disk surface. The hard disk drive has a composite magnetic head (read/write head), which comprises two devices: a read head and a write head. The read head reads data stored on the magnetic disk, whereas the write head writes data onto the magnetic disk. The magnetic head is mounted on an actuator mechanism, which is oscillated by a VCM (voice coil motor).
When the magnetic head writes data onto the magnetic disk, a specified current flows to the write head to magnetize a magnetic film that is formed on the magnetic disk. When data is written on the magnetic disk, new data frequently overwrites the existing data. The overwrite characteristic, which indicates whether an overwrite is properly performed, depends on the current value for a data write performed by the write head (write current value). It is known that when the write current value is small, the overwrite characteristic deteriorates because the magnetic pattern of previously written data cannot be adequately remagnetized. If, on the other hand, the write current value is excessively great, a squeeze problem arises in remagnetizing the magnetic pattern of an adjacent track. Further, the read signal characteristics may frequently deteriorate depending on the write current value. It is therefore necessary that the write current value be properly set.
However, the optimum write current value cannot be uniquely determined. For example, it is known that the above-mentioned overwrite characteristic varies with the hard disk drive installation environment parameters, especially the temperature. More specifically, the Hc or coercivity of a magnetic film formed on the magnetic disk surface increases with a decrease in the temperature. Therefore, if it is assumed that the write current value is constant, the lower the temperature, the worse the overwrite characteristic.
To improve the overwrite characteristic in a low-temperature environment, Patent Document 1 proposed a technology for providing a greater write current value in a low-temperature environment than in a high-temperature environment.
A differential amplifier circuit has been put to practical use with recent hard disk drives in order to supply a positive voltage and negative voltage to a head amplifier to improve the signal-to-noise ratio of a read signal output from the read head. Accordingly, write operations performed by the write head have also begun to use a positive voltage and negative voltage. The advantage provided by supplying positive and negative voltage to the write circuit in the head amplifier is that the write speed can be increased.
This type of hard disk drive receives positive voltage from a host computer and supplies the positive voltage to the head amplifier's write circuit while a circuit for the hard disk drive converts the positive voltage to a negative voltage and supplies the resulting negative voltage to the head amplifier's write circuit.
Japanese Patent Laid-open No. 5-258215
The write circuit of the above-mentioned hard disk drive is now described. This write circuit reverses the write current direction and provides voltage drive even at the time of constant current drive by directly supplying the negative voltage, which is supplied to the head amplifier's write circuit, to the write head via a variable internal limiting resistor. If an unduly high negative voltage is applied to the head, the amount of electrical current overshoot increases at the time of write current direction reversal, causing an equivalent increase in the write current. Therefore, the internal limiting resistance is adjusted to minimize the amount of overshoot for acquiring the necessary electrical current reversal speed, thereby ensuring that the voltage applied to the head is lower than the supplied negative voltage. In this case, the power consumed by the internal limiting resistor turns to heat and does not contribute to a data write at all. Therefore, a technical problem has arisen so that a voltage-driven write circuit consumes more power although it provides an attractively high speed.
Further, the positive voltage that the hard disk drive receives from the host computer is unstable when compared to the negative voltage generated inside the hard disk drive. Therefore, when the electrical current direction reverses, the above-mentioned type of circuit uses a stable negative voltage via a low-resistance path. However, even if the positive voltage drops, the positive voltage applied to the head terminal on the opposite side lowers. Consequently, the amount of overshoot decreases to a certain extent (although the resistance for current limiting is fixed at a high level). As a result, the write current may equivalently decrease so as to incur a data write error.